Generally, clean room arrangements have a clean room, an air feed chamber formed in an upper portion of the clean room and a recirculation chamber formed in a lower portion of the clean room. The air feed chamber is provided with a filter and feeds clean air into the clean room through the filter. The recirculation chamber is provided with a grating and sucks the clean air through the grating. Therefore, the clean air introduced into the clean room from the air feed chamber via the filter goes down and enters the recirculation chamber. Then, the clean air is recirculated to the air feed chamber. On the way to the air feed chamber, external air for the ventilation is added to the circulating clean air if necessary, and such a combination is recirculated into the clean room.
Various types of clean room arrangement are proposed. FIG. 5 of the accompanying drawings shows one of such arrangements. An air conditioner a is placed outside a clean room f and used to recirculate the clean air. A filter e extends in an upper portion of a clean room arrangement 1 and defines an air feed chamber d above the filter e. A clean room f is defined below the filter e. In other words, the filter e serves as a ceiling of the clean room f. A grating g extends in a lower portion of the clean room arrangement 1 and is used as a floor of the clean room f. A recirculation chamber h is defined below the grating h whereas the clean room f is defined above the grating h. An outlet of the recirculation chamber h is connected to an inlet of the air conditioner a by a recirculation duct i. An outlet of the air conditioner a is connected to the air feed chamber d by an air feed duct c. A blower b of the air conditioner a forces the air to flow into the air feed chamber d through the air feed duct c and the air is introduced into the clean room f after it is filtered by the filter e. The clean air entering the clean room f descends into the recirculation or air recovery chamber h, as indicated by the arrows in the drawing. The clean air flows through the grating g as it enters the recirculation chamber h. Then, the clean air returns to the air conditioner a through the recirculation duct i.
FIG. 6 shows another clean air arrangement. The air conditioner a is joined with the clean room f. The clean air from the blower b directly enters the air feed chamber d from the outlet of the air conditioner a. The outlet of the air conditioner a communicates with the upper portion of the upper portion of the clean room f. Likewise, the clean air from the recirculation chamber h directly flows into the inlet of the air conditioner a. The lower portion of the clean room communicates with the inlet of the air conditioner a.
FIG. 7 illustrates an arrangement which has a blower j equipped with filters. The clean room f is defined in the clean room arrangement 1 with the recirculation space k being formed around the clean room f. The clean air is directly introduced into the clean room f by the filter-provided blower j and then expelled to the recirculation chamber h from the clean room f via the grating g. The clean air then flows upward in the recirculation chamber h and returns to the air feed chamber d.
These conventional arrangements have following problems:
If an air flow rate of the blower is raised in order to obtain high cleanliness in the clean room f, the pressure loss across the filter becomes large and the power for the blower becomes large. In addition, the recirculation of the clean air by the blower causes a non-homogeneous pressure profile in the recirculation system which in turn causes a drift current in the clean room. On the other hand, if the air flow rate of the blower is lowered and high cleanliness of the clean room is attempted, a turbulence is generated in the clean room and an ascending current is locally produced in the clean room. Therefore, high cleanliness cannot be expected.